This invention relates to a fuel control device for a diesel engine of direct jet type having unit injectors.
A conventional fuel control device, as shown in FIG. 1, comprises: a gear pump 2; a governor 4; a fly weight 5; a mechanical variable speed (MVS) governor 10; a shut-off valve 13; and an injector 15. The fuel control device has two important control functions. One of the functions is that fuel is delivered, under pressure, out of a fuel tank 1 by means of the gear pump 2, and a fuel pressure is regulated for an engine speed by the governor 4 with the balance of three elements, i.e. the fly weight 5 coupled to the rotation of the engine, a governor spring 6 and the fuel pressure, thereby to determine the acceleration horse power, maximum horse power and maximum torque or torque curve of the engine. The other function is that, irrespective of load applied to the engine, the MVS governor 10 maintains an engine speed constant according to the position of a throttle lever 11 with the balance of a fuel pressure provided by the gear pump 2 and an MVS governor spring 12.
However, the above-described conventional fuel control system is disadvantageous in that it is considerably difficult to change characteristic curves such as a torque curve and a horse power curve as desired because it has various combinations as to the characteristic of the governor spring 6, the size of a button 7, a governor plunger 8, etc.
On the other hand, a diesel engine with a supercharger suffers from the following trouble: When the engine is quickly accelerated, then the speed of the supercharger cannot follow the increasing speed of the engine, as a result of which the amount of suction air becomes insufficient, i.e. the amount of oxygen becomes short, and therefore a large amount of black smoke is discharged from the exhaust pipe.
In order to overcome this difficulty, heretofore a method utilizing the pressure in the intake manifold is employed. That is, when the pressure in the intake manifold is low, the amount of fuel jetted by the injector (hereinafter referred to as "an amount of jet fuel" when applicable) is reduced, to prevent the production of black smoke at the time of acceleration.
However, the method is still disadvantageous in that it is difficult to control the amount of jet fuel with high accuracy, and accordingly it is difficult to positively prevent the production of black smoke.